Methyl carbamate (MC) has been recently studied by the National Toxicology Program for chronic toxicity and carcinogenicity. MC was found to be toxic to rats but had no effect on mice. The present study was designed to investigate mechanisms of action which can account for the observed species specificity in MC toxicity. Results of these studies indicate that although MC is readily absorbed and rapidly distributed to all tissues, in both rats and mice, mice are much more efficient in clearing MC and/or metabolites from the tissues than rats. Within 72 hours after administration greater than 95% of the dose is eliminated by mice while in rats over 50% of the dose is still present in the tissues.